1. Field of the Invention
The present invention relates to a drying device and a drying method for drying a photosensitive layer of a photosensitive planographic printing plate using infrared rays.
2. Description of the Related Art
Photosensitive planographic printing plates are produced in the following manner. At least one surface of an aluminum web, which is a belt-shaped aluminum thin plate, is grained, and a photosensitive coating liquid containing photosensitive resin or thermosensitive resin is applied to the surface and is dried to form a photosensitive layer.
For example, in Japanese Patent Application Laid-Open (JP-A) No. 8-296962, as shown in FIG. 4, items to be heated are continuously transported on a conveyor 100 and heated, and far infrared heaters 102 are arranged parallel to and above and below the conveyor 100, so as to prevent temperature variation with respect to the items being heated.
In JP-A No. 2002-14461, as shown in FIG. 5, a far infrared emitting device 106 is arranged downstream of a hot air drying device 104. The far infrared emitting device 106 is composed of a far infrared heater 108 in which ceramic material is used to emit far infrared rays.
The surface temperature of the ceramic material in the far infrared heater 108 is 300° C. or more (λmax: 5.1 μm), at which drying efficiency is superior to that of a hot air system, and not more than 800° C. (λ max: 2.7 μm), which does not include wavelengths of 1 μm or less. The far infrared heater 108 is adapted to heat a photosensitive layer and an aluminum plate 110.
In JP-A No. 2000-329463, the wavelength area range within which a liquid can be dried efficiently is 1 to 30 μm, and a far infrared lamp which emits infrared rays of predominantly 2 to 7 μm is optimal for drying a coating film
With infrared rays, heating efficiency is better in a low-wavelength range (not more than 2 μm), however when an aluminum web formed with a photosensitive layer is heated by infrared rays in low-wavelength range (not more than 2 μm) with satisfactory heating efficiency, a photosensitive object on the aluminum web will become fogged. For this reason, the aluminum web is generally heated by far-infrared rays which are not in the low-wavelength range (for example, JP-A No. 2002-14461); however, this deteriorates the heating efficiency.
In JP-A No. 2000-35279, therefore, which discloses only a far infrared drying furnace, it takes time to reduce residual solvent after a coating film is adhered, and thus the drying efficiency is deteriorated. For this reason, a heated roll as well as the far infrared drying furnace is used, and a hot-air furnace is also used, in order to compensate for the deterioration of the heating efficiency due to use of far-infrared rays.